Little babies vet visit

Right now at the moment I'm fostering two little babe kittens. One I'm keeping and one I'm looking for a home. But my sister brought in her pets when she came to live with us and since then, both of the kittens have gotten invested with fleas and one of them has gotten incredibly sick. The othero ne is starting to get sick. Their cat and dog has even gotten the two other cats we own sick. But right now, my main goal is to get enough money to help take at least one of the kittens to the vet. Last time I went, the bill for one of them was around $260 so I'm hoping to raise at least $300 just in case, $400 at most. If I could raise enough to take all of them to the vet, that would be wonderful, but right now my goal is just to get the sickest one better. Anything will help!